Air supply outlets such as are used for distributing fresh air in an air circulating system, usually incorporates some form of damper for controlling the flow of air through the outlet. Such air outlets may be of various shapes. When the air outlet is located in the ceiling, particularly of domestic, or office space or commercial space, or the like, a circular form of air distribution outlet is particularly preferred. This form of outlet is usually connected by means of a duct system of generally circular cross section.
The design of a damper for use in a connection with such circular duct and circular outlet, presents certain problems. It must be adaptable to progressively open and close the circular opening, and at the same time it must be accessible from the building space beneath the air outlet and ceiling itself.
One form of such a damper which is particularly suitable for the purpose is shown in U.S. Pat. No. 3,592,240. That patent discloses a damper having two generally semi-circular panels, which are hinged to swing upwardly and downwardly about a central strut.
A worm and linkage, is mounted below the strut, and connects between the strut and the hinged panels.
A suitable tool such as a screwdriver or the like may be inserted to rotate the worm and thus adjust the two panels upwardly and downwardly.
This device works effectively and has proved to be popular and satisfactory.
There are however certain disadvantages with this system. Fire insurance and building code regulations are requiring much higher standards of resistance to heat and fire, particularly in the construction of ceilings in such buildings. A principle area of weakness in such ceilings occurs at each air outlet. The ceiling itself may be constructed of panels which are substantially fireproof or are at least heat resistant for a sufficient length of time to meet the regulations. However, each air outlet constitutes a relatively substantial opening through such ceiling. These openings provide an easy passage way for heat and possible flames, through the ceiling. Thus although the ceiling fabric itself may have the necessary fire rating which substantially negates the effectiveness of the ceiling in a fire situation.
Thus in buildings where the construction code or regulations call for a fire rated ceiling, it is highly desirable to provide some form of automatic fire damper in the ducts immediately above each air outlet. Such fire dampers are sensitive to heat and will close automatically in response to a pre-determined temperature.
Fire dampers of rectangular design are well known in the art. Essentially, all that is required is simply to place a fire damper in the duct above the air outlet and control damper of the type shown in the U.S. Patent referred to above.
In practice however this greatly increases the cost of construction. In addition, the installation time required is much greater than the time required for installation merely of the outlet and control damper itself. A further problem is that the location of a fire damper of conventional construction on top of such an air outlet and a control damper, creates an excessive height above the ceiling. This may in fact interfere with the dead space between the ceiling, and the floor slab of the floor next above in the building.
Most of the existing fire dampers incorporates some form of heat fusible link, and one or more blades which is spring loaded, and is held open by means of such a link. When the link becomes heated, it melts and releases the blades. The blades then snap closed, thereby closing off the duct.
It might at first appear feasible to modify the damper shown in U.S. Pat. No. 3,592,240 to include a spring and a fusible link.
However, in practice it is found that this will not be satisfactory. The location of the worm, and operating linkage on the strut below the level of the panels, causes obstruction on the underside of the panels. The inclusion of some form of heat fusible member in such linkage will therefore present serious difficulties. The linkage will tend to obstruct the closure of the panels, in response to a fire situation.
Nevertheless, it is readily apparent that if the control damper can also be used as a fire damper, there would be substantial economies achieved in the cost of materials and also even greater economies is the cost of installation. In addition, the problems of obstructing the dead space between the ceiling and the floor slab will also be eliminated.
On the other hand, in providing such a multi-mode damper, it is essential to avoid increasing the cost to the point where when it is used merely as a control damper it has a cost greater than prior art control dampers.
It is therefore desirable to provide a control damper, which may be used as a fire damper, where building regulations have this requirement, and which may be used as a control damper, where this requirement is not present.